Tom Coughlin’s poor, underestimated defending-Super-Bowl-championship team had a chance after all.

Four days after Coughlin’s “Nobody-gives-us-a-chance” statement inspired endless rolling of the eyes, his team showed why it was so laughable Sunday in a 26-3 romp over the 49ers at Candlestick Park.

The Giants, who entered as six point underdogs, handed the 49ers their worst loss of the 22-game Jim Harbaugh era and didn’t allow San Francisco to enter the red zone, collect a sack, force a turnover or score in the game’s final 47 minutes.

Unlike last season’s overtime win in the NFC Championship Game, the Giants left no doubt about who was the better team Sunday.

Asked if he was humbled, cornerback Carlos Rogers said the 49ers, who had outscored opponents 79-3 the previous two weeks, had been reminded of their standing in the league’s pecking order before kickoff.

Safety Donte Whitner said the desire to take down the champs might have undone the 49ers, who fizzled after a fast start.

In the second half, New York running back Ahmad Bradshaw had 93 of 116 yards and averaged 5.8 yards a carry. San Francisco allowed its most rushing yardage (149 yards) in 27 games and Bradshaw became the first opposing running back to post a 100-yard performance since Tennessee’s Chris Johnson on Nov. 8, 2009.

Jim Harbaugh. (AP)

“(We) possibly got too high,” Whitner said. “A lot of people talking about redemption and this and that. Really, it’s game six of a 16-game schedule. We possibly set ourselves up for that.”

While the Giants were establishing the run, the 49ers, owner of the NFL’s leading rushing attack, were abandoning it, with disastrous results.

After the first quarter, the 49ers led 3-0 and had outgained the Giants, 120-25, with a balanced attack (13 passes, 9 runs). In the final three quarters, however, they had eight runs and Frank Gore (8 carries, 36 yards) didn’t have a carry in the game’s final 39 minutes.

A week after players hailed offensive coordinator Greg Roman as a “mad scientist” and “evil genius” following a franchise-record 621-yard performance, he had a hand in a team-wide collapse.

“The plan wasn’t the best plan,” Harbaugh said. “And we’ll work to make a good one this week. Wasn’t a great day for any of us.”

The plan appeared particularly poor after Alex Smith tossed three interceptions in a stretch of eight attempts spanning the second and third quarters. Smith, who entered with three interceptions in his past 378 attempts, said the sprained middle finger on his throwing hand wasn’t a factor as he posted a 43.1 rating, his worst in 33 starts.

With the 49ers trailing 17-3, Smith threw interceptions to safety Antrel Rolle on San Francisco’s first two drives of the third quarter. The back-to-back picks allowed the Giants to collect two field goals while gaining just one yard en route to grabbing a 23-3 lead.

On his final interception, Smith said he was duped by Rolle, who jumped the route on a pass intended for Michael Crabtree.

Said Smith: “I didn’t see it.”

Said Rolle: “I could tell at times we had him a little rattled.”

As for the game’s other signal-caller, Eli Manning, he was barely touched.

After taking a pounding in the NFC Championship Game (6 sacks, 12 hits), Manning wasn’t sacked and took just one hit, none in the final three quarters.

At one point in the second quarter, Manning completed nine straight passes for 151 yards, a stretch highlighted by his six-yard scoring dart to wide receiver Victor Cruz to give New York a 7-3 edge.

But he ended with a pedestrian stat line (193 yards, 87.4 rating), in part because the quarterback termed a “magician” by Harbaugh earlier in the week didn’t need to pull off any rabbit-out-of-hat heroics.

With a comfortable lead, the Giants ran on 26 of their 36 second-half plays and averaged 4.8 yards a carry.

“It was great,” Manning said. “That’s what you want to be able to do. That’s when the offensive line just takes over the game and you can run the ball.”

In the other locker room, the 49ers were searching for a silver lining and they found one in their schedule.

With a home date against the Seahawks (4-2) on Thursday night, they would be forced to forget about Sunday’s shocker sooner than usual.

“If we let this one linger, it can go into that game and we don’t need that,” Whitner said. “We don’t need two (defeats) in a row, so we have to quickly forget about this one.”